To reiterate what's been said...
I would not want to be single-homed to Cogent. They're fine (and
generally useful and a reasonable use of your operating money) in a blend.
I'm not familiar with 123.net, but looking briefly at them, they appear
to be a regional blend. Much preferable compared to your other option
assuming they competently operate their network.
FWIW, I wouldn't WANT to be single-homed to anyone, but I'll do it when
it's the right choice.
If you have to be single-homed, you really have to go with a quality
upstream, and you're going to pay for it. If you have the volume and
connectivity to be multi-homed, do it. It'll be better in just about
every way.
--
Brandon Martin
